A computed axial tomography scan, better known as a CAT scan or CT scan, is used to image the internal organs of the body using multiple x-ray beams taken successively from multiple angles. A lung CT scan is used to diagnose and monitor diseases that may have a nonspecific appearance on conventional chest x-ray. Doctors also use a lung CT scan to guide them during biopsy, in which a sample of lung tissue is obtained, to be examined under the microscope.
- Skill level:
Things you need
- Patient chart
- Lung CT scan films
- X-ray film viewer (negatoscope)
- Atlas of human anatomy
Review the patient's chart. Read the patient's clinical history and take note of the pertinent physical examination findings. Important data include the presence of cough, fever, shortness of breath and blood-tinged sputum. Find out if the patient is a smoker. These will guide you regarding what abnormalities to look for in the lung CT scan.
Put up the patient's lung CT scan films on the negatoscope. Make sure that the name, age and sex of the patient indicated on the film are identical to the ones that are indicated on the patient chart. If the patient has previous lung CT scan films, put them up as well.
Identify the orientation of the lung images on the film. The latest CT scans can display images of the lung taken in three orientations, depending on how the image slices were obtained: • Axial view: from top to bottom • Coronal view: from front to back • Sagittal view: from side to side The image slices are usually obtained at 1-cm intervals. This is sufficient to show lung abnormalities in most patients. However, in cases when the suspected lesion such as a pulmonary nodule is small, you would want thinner, 1- to 5-mm cuts obtained by high-resolution CT.
Identify the structures of the lungs guided by your atlas of human anatomy. Proceed systematically so that you don't miss any abnormalities. For example, you may choose to go from top to bottom and from periphery to centre of each lung, or the other way around.
Inspect the hilum. This is where the bronchi (large airways), pulmonary arteries and veins (major blood vessels), and nerves enter. Look for changes in their diameter as well as for enlargement of lymph nodes.
Inspect the lung parenchyma. Trace the branching of the airways. These are white to grey dots and lines against a black background, which represents air on the CT scan. Normally, the airways taper off as you go from the centre to the periphery of the lung. The airways may become more prominent than they are supposed to, or they may disappear when a lung segment has collapsed. You may also see a mass that disrupts the normal anatomy of your lung tissue.
Inspect the pulmonary pleura. The pleura covers your lungs. In disease states, you may be able to observe pleural thickening and accumulation of fluid such as blood or pus on the dependent portions of the lung. Masses may also originate from the pleura.
Write your diagnosis. Mention your abnormal findings, as well as the pertinent negative findings. If you see focal abnormalities on the lung CT scan, mention their location and take their measurements, if possible.
Tips and warnings
- Most lung CT scans are now available in a digital format known as DICOM, which stands for Digital Imaging and Communications in Medicine. Using a DICOM viewer installed on your computer, you would be able to visualise the lung structures better and adjust the image settings as necessary.
- Don't mix up old and new films, and CT scan films of different patients. Otherwise, you may be sued for providing the wrong CT scan reading.
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